The trophoblast originates from the outer cell mass of the blastocyst, which differentiates to form the placenta and supporting embryonic structures. This layer is crucial for implantation into the uterine wall and establishing nutrient exchange between mother and embryo. The inner cell mass, by contrast, forms the embryo proper and the embryonic germ layers (endoderm, mesoderm, ectoderm). Understanding the origin of the trophoblast is essential for recognizing disorders like ectopic pregnancies and placental abnormalities.

Reference: Gray's Anatomy, Richard L. Drake, Edition 42.